BBC News
By Lina Shaikhouni
image copyrightGhaith al-Zaanin
image captionDr Ayman Abu al-Ouf (R) dedicated his life to treating patients and training students, Dr Ghaith al-Zaanin (L) said
Without warning, an Israeli air strike destroyed the four-storey building in the Gaza Strip where Dr Ayman Abu al-Ouf lived early on Sunday.
The doctor, who was head of internal medicine at the Palestinian territory s main hospital, was killed along with 12 members of his extended family.
They included his mother and father, his wife Reem, and their 17-year-old son Tawfik and 12-year-old-daughter Tala. This is a really big loss not just for us personally because we knew Ayman - this is also a loss for his patients and students, Dr Ghaith al-Zaanin, a close friend and former colleague who lives in Canada, told the BBC.